Small Office Service Serial Router Connects Internal Stations

Small Office Service • Serial Router Connects Internal Stations to Shared Broadband Access Service Serial Router Shared Broadband Line Small Office ISP

Small Office Service • Serial Routers are Very Simple – One or more ports to connect the serial port to the LAN – One port to connect to the high-speed access line, which is serial – Much less expensive than general-purpose routers because no complex router forwarding decision caused by multiple possible output ports Serial Router

Small Office Service • Serial Router Connects Internal Stations to Shared Broadband Access Service – Companies with several stations pay much more for line than when connecting a single PC – Each machine gets its own IP address via DHCP – Serial router may be a user PC with added software – Often, router is called a gateway (the old name for router)

Connecting Two PCs at Home • Physically, One PC (the Gateway PC) Connects to the Hub or Switch and to the Broadband Line – Gateway (router) PC needs two Network Interface Cards, one for hub, one for broadband modem Hub or Switch NIC ADSL/Cable Modem Gateway PC Broadband Line to ISP

Connecting Two PCs at Home • Gateway PC Needs Gateway Software – On NIC to broadband line, acts like a single station – Gets temporary IP address from ISP DHCP – Sends and receives to ISP using this IP address Gateway PC Send, Receive with Temporary IP Address

Connecting Two PCs at Home • Gateway PC Needs Gateway Software – Each PC is set up with a permanent IP address – So gateway PC has two addresses, one bound to each NIC Gateway Program Permanent IP Address Temporary IP Address

Connecting Two PCs at Home • Gateway Software Does Network Address Translation (NAT) – When a PC sends using permanent IP address – Gateway software replaces source IP permanent address with temporary IP address ISP expects Gateway PC Permanent IP Address Temporary IP Address

Connecting Two PCs at Home • Gateway Software Does Network Address Translation (NAT) – When a PC receives – Gateway software replaces ISP temporary IP destination address with receiver’s permanent IP address, passes on to PC Gateway PC Permanent IP Address Temporary IP Address